There are used recording and/or reproducing apparatuses which record information signals to a disc-shaped recording medium. As a disc-shaped recording medium used in this kind of recording and/or reproducing apparatuses, there are optical discs such as a CD (Compact Disc), a CD-R (CD-Recordable), a CD-RW (CD-ReWritable), a DVD (Digital Versatile Disc), and an MD (Mini Disc) being a magneto-optical disc which is 64 mm in diameter.
The recording and/or reproducing apparatuses using various kinds of disc-shaped recording media, which have been described above, have a recording and/or reproducing unit which corresponds to a disc-shaped recording medium to be used.
A disc player which uses an optical disc of an MD as a recording medium includes a disc rotation drive mechanism 103 for driving or rotating an optical disc 102 housed in a disc cartridge 101, an optical pickup 104 for reproducing information signals from the optical disc 102 driven by the disc rotation drive mechanism 103, a support mechanism 107 having a pair of guide axes 105, 106 for movably supporting the optical pickup 104 along the radial direction of the optical disc 102, and a pickup shift mechanism 108 for shifting the optical pickup 104 supported by the support mechanism 107 along the radial direction of the optical disc 102, as shown in FIG. 1 and FIG. 2. The respective mechanisms are arranged in a mechanism chassis or a mecha-chassis 110 arranged in the disc player body, as shown in FIG. 1 and FIG. 2.
The disc rotation drive mechanism 103, which drives the optical disc 102, has a disc table 111 onto which the optical disc 102 is placed, and a spindle motor 112 for driving or rotating the disc table 111, as shown in FIG. 3. The optical pickup 104 has an optical block 114 for condensing an optical beam emitted from a light source using an objective lens 113 and irradiating thus condensed optical beam to the signal recording surface of the optical disc 102, and for receiving a returning optical beam reflected by the signal recording surface of the optical disc 102 using a photodetector, and a biaxial actuator 115 for shifting the objective lens 113 along the focusing direction parallel to the optical axis of the objective lens 113 as well as along the tracking direction perpendicular to the optical axis of the objective lens 113 based on detection signals detected by the photodetector. The support mechanism 107 has the guide axes 105, 106 for movably supporting the optical block 114 of the optical pickup 104 along the radial direction of the optical disc 102. The pickup shift mechanism 108 has a lead screw 116, a gear group 117 consisting of a plurality of gears, and a shift motor 119 for shifting the optical pickup 104, which are arranged on the mecha-chassis 110. The shift motor 119 drives or rotates the gear group 117 to rotate the lead screw 116 engaged with the gear group 117 so as to shift the optical pickup 104 which has an engagement pin 118 engaged with the lead screw 116, with the optical block 114 guided by the guide axes 105, 106.
With thus configured disc player, when the optical disc 102 is driven by the disc rotation drive mechanism 103, the optical pickup 104 supported by the support mechanism 107 is shifted by the pickup shift mechanism 108 along the radial direction of the optical disc 102, while the optical pickup 104 irradiates an optical beam to the signal recording surface of the optical disc 102 to scan the signal recording area thereof Then, the photodetector of the optical pickup 104 detects a returning optical beam reflected by the signal recording surface of the optical disc 102 to read information signals recorded on the optical disc 102.
In the conventional disc player, the pickup shift mechanism 108, which shifts the optical pickup 104 along the radial direction of the optical disc 102, generally converts rotational driving force of the shift motor 119 to linear driving force by means of the gear group 117 and the lead screw 116. Therefore, in thus configured disc player, the number of parts or components are inevitably increased, which raises various problems. Specifically, space for arranging the shift motor 119, gear group 117, etc. is required to be prepared, which makes it difficult to further reduce the disc player in size. Since the number of parts is increased, undesirably, cost required for those parts is caused to be high as well as the number of steps in the assembling process is caused to be increased. Moreover, since rotational driving force is converted to linear driving force, conversion efficiency is low, which undesirably requires large power consumption. Furthermore, the problem of noise due to the shift motor 119, gear group 117, lead screw 116, etc. has been pointed out.
Especially, as shown in FIG. 1 and FIG. 2, in the disc player which employs the shift motor 119 and the gear mechanism for transmitting rotational driving force of the shift motor 119 to linear driving force to shift the optical pickup 104, it is necessary that a plenty of parts be arranged on the mecha-chassis 110. Thus, a wide area of the mecha-chassis 110 is used to arrange the mechanism for operating the optical pickup 104. In result, mechanisms and the number of parts to be arranged on the mecha-chassis 110 are restricted. Mechanisms and parts which cannot be arranged on the mecha-chassis 110 have to be arranged on other region of the main body of disc player, which also makes it difficult to reduce the disc player in size.
Furthermore, the pickup shift mechanism 108, which has the shift motor 119 for shifting the optical pickup 104, becomes comparatively thick, which should be taken into consideration to reduce the thickness of the disc player itself.
There is also used a disc player which uses, as a shift motor for shifting an optical pickup, a linear drive motor which performs linearly driving instead of using a rotational drive motor. However, it is difficult to adopt such a disc player to a portable type disc player since driving power is increased and its optical pickup has difficulty in keeping itself at constant positions when the operation is stopped.
A disc player performs, using a biaxial actuator, the focusing control to bring a focal point of an objective lens to the signal recording surface of an optical disc while shifting the objective lens along the focusing direction parallel to the optical axis of the objective lens, and the tracking control to bring a beam spot of an optical beam condensed by the objective lens to recording tracks of the optical disc while shifting the objective lens along the tracking direction perpendicular to the optical axis of the objective lens. A biaxial actuator for performing the focusing control and the tracking control used in the conventional disc player is complicated in its configuration and takes time in assembling parts thereof, which leads to high manufacturing cost.
Furthermore, in the conventional disc player, when the optical pickup is shifted along the radial direction of the optical disc, the position of a beam spot of an optical beam to be received by a photodetector is deviated since the objective lens swings along the radial direction of the optical disc. Thus, there is undesirably generated offset in detection signals. Also, when the objective lens is caused to swing, a skew of the object lens itself is generated, which may deteriorate detection signals.
Thus, it is necessary for the conventional disc player to correct detection signals in view of the offset due to the swinging of the objective lens, which may complicate the mechanism for performing the tacking control. Furthermore, power to keep the view direction of the object lens constant is necessary, which may require power consumption.